Telephone system



M. B. lvlcDAvn-T 2,138,186

TELEPHONE' SYSTEM Filed Nov. 25, 1935 5 Sheets-Sheet vl Nov. 29, 1938.

Nov. 29, 1938. M.v B. McDAvlTT y TELEPHONE SYSTEM 5 Sheets-Sheet 5 FiledNov. 25, 1955 Il MEQ Cil Patented Nov. 29, 1938 PATENT OFFICE YTELEPH01-IE.SYSTEM Marcellus Baui McDevitt, White Plains, N. Y.,

assigner to American Telephone and Telegraph Company, a corporation ofNew York Application November 23, 1935, Serial No. 51,314

6 Claims.

This'invention relates to telephone systems in a subscribers linebetween the point where and particularly to systems of the class usingautomatic switching apparatus for establishing connections.

The objects of the invention are to facilitate changes in the,Voperating conditions of subscribers lines without altering the4individual equipment normally `provided for such lines; to enable anyline to be'changed from one operating condition to another by a simplewiring change Vat the distributing frame; to provide for the guardingoi' a telephone line against seizure by one switch while another switch,such as a line finder, is seeking the line; and otherwise to improvesystems of this character.

Systems have been devised heretofore in which a subscribers line, whenin a calling condition, is rendered unselectable toga connector switchduring the interval a line finder is seeking the line in response to thecalling condition. This hasv been accomplished by relay connections 4inthe line circuit, thus requiring a different type of individual linecircuit for those lines that are to be guarded than that used for otherlines in the exchange that do not need the guarding feature. One reasonfor guarding the line during the interval mentioned is to prevent acalling connector from seizing the line and tripping the ringingcurrent-applying mechanismVV without notice to the calling party thathis call has failed. Also, in case of a private branch exchange group,the call may fail under these conditions although succeeding trunks inthe same group are idle.

According toa feature of the present invention an auxiliary controlcircuit isr arranged to be connected to the conductors of aY subscribersline Without disturbing the regular line circuit individual to the line,and which auxiliary circuit when so connected cooperates with the linecircuit to control the operating conditions of the line and central oiceapparatus. I'his'auxiliary circuit is connected to one side or member ofthe intermediate distributing frame where it can be included readily, bymeans of cross-connecting wires, in circuit with the subscribers lineconductors and also in circuit with the line circuit individual to suchline. In this way the auxiliary circuits can be permanently connected tothe frame, and by a simple change of the cross-connecting wires they maybe connected respectively to any of the subscribers lines that requirethe additional control features provided by the auxiliary circuits.Moreover, all lines can be installed uniformly with their regular linecircuits, and these require no change in case it is found desirablelater either to add or toremove one of the auxiliary circuits.

Another feature of the invention is an arrangement in which a line.control relay is connected tential on the connector terminals of theline while the line nder is hunting for the line in response to acalling condition. After the line finder finds the line and the cut-olirelay operates to disconnect the line relay. a circuit is closed forshunting the control relay so as to exclude it from the subscriberspulsing circuit extending to the selector switches in the exchange andalso to exclude it from the talking circuit which will later becompleted. In one embodiment of the invention the control relay is alsoshunted to remove it from the talking circuit when the subscribers lineis engaged as a called line.

The foregoing and other features of the invention will bevmor'e fullydescribed in the' following specication and will also become moreappar-V ent from the appended claims.

' The specification should be taken in connection with the accompanyingdrawings, in which: Figure l shows a number of subscribers line circuitsand auxiliary circuits and illustrates the i circuit and also a-modiflcaton ofthe distributing trame arrangement.

A In order to achieve the objects and features of this invention,advantage is taken of the distributing frames at the central cnice. Inoliices of appreciable size itl is customary to provide both amainl-distrilouting frame and an intermediate vdistributing frame. Thesubscribers lines entering the office appear rst on the main frame. Fromthere they extend to the intermediate frame, and from this latter framethey are connected to the 'individual line circuits, to thenon-numerical switches, such as nders, for outgoing calls', and toj thenal or connector switches 'for incoming calls. Each frame comprises twoparts, a vertical side and a horizontal side, and the variousconnections between the two sides of each frame and between frames aremade by `iumper wires and cables which may be changed. from vtime totime as occasion requires. It is, of course, desirable to avoid as muchas possible the necessity of making these jumper` changes and tofacilitate the work of makilslg such changes when they do becomenecessary. However, it is also desirable to take full advantage of therelative ease with which jumper connections can be made where thislleads to a saving in the amount of equipment needed in the oflce.

As explained above, it is desirable to guard some lines, particularlyprivate branch exchange lines, from seizure by a connector switch whilethey are in a calling condition and before the line finder has completedits hunting operation and guarded the calling line. Yet it would beexpensive to provide al1 line circuits in the oice with extra equipmentto secure this feature, where some of the lines do not at the timerequire the service and may never require it in the future, and the moreeconomical way is to equip the oii'ice with a suilcient number ofauxiliary line circuits which may be associated with any desiredsubscribers line in the exchange by making jumper Wire connections suchas those described above. This makes it possible for any line in theoiiice to be converted by a simple wiring change performed at thedistributing frame. y

Referring now Vto the drawings and first to Fig. 1, two subscriberslines A and B are shown entering the exchange and appearing on thevertical side I of the main distributing frame. From the side the linesA and B are connected to the horizontal side 2 by jumpers 3 and 4,respectively; and from the horizontal side of the main distributingframe these lines are connected to the horizontal side 5 of theintermediate distributing frame by means of the cable pairs 6 and 1,respectively. The line A, for example, is represented on the side 5 ofthe intermediate frame by terminals 8, 9, I and II, and the cable pair 6is wired to the terminals 8 and 9. Similarly, line B is represented byterminals I2, I3, I4, and I5, and the cable pair 'I is wired toterminals I2 and I3. All other subscribers lines entering the exchangeare wired in a similar manner to the main distributing frame and fromthere to the horizontal side of the intermediate frame. At theintermediate frame each subscribers line is further connected to its ownindividual line circuit and to a non-numerical switch, such as a linender, for out-going calls and is also connected to the contact banks ofthe connector switches for incoming calls. The individual line circuits,such as line circuits L and L-I for lines A and B, are connected to thevertical side I6 of the intermediate distributing frame. The linecircuit L appears in terminals I1, I8, I9 and 20, and line circuit L-Iappears in terminals 2|, 22, 23 and 24. These line circuits include theusual relays and equipment; the line circuit L comprises a line relay 25and a cut-off relay 26, and the line circuit L-I comprises a line relay28, and a cut-oil" relay 29. The message registers 21 and 3D are alsoindividual to lines A and B,

respectively. n Y Y As explained hereinbefore, the exchange is alsoequipped with a suitable number of common auxiliary line circuits. Twoof these are illustrated, circuits AL and AL-I, and they too areconnected to the vertical side of the .intermediate frame. The circuitAL includes a line control relay 3| and a relay 32 and appears interminals 33, 34, 35, 36, 31, and 38 on the frame member I6. In asimilar manner the auxiliary line circuit AL--I comprises relays 39 and40 and appears in terminals 4I, 42, 43, 44, 45 and 46. Any subscriberslines may be connected directly to its individual line circuit by usingone arrangement of jumper wires, or it may be connected to itsindividual line circuit through one of the auxiliary line circuits byusing a different arrangement of jumper wires. The line A is shownconnected directly to its individual line circuit L and to the terminalsin the line finder F. In this case a jumper 48 joins the terminals 8, 9,and I8 of the horizontal side 5 withthe terminals I1, I8, and `I9 on thevertical side I6 of the intermediate frame. The line B is shownconnected to its individual line circuit L-I through the auxiliary linecircuit AL-L In this case a jumper 49 joins the terminals I2, I3 and I4on the horizontal side and the terminals 4|, 42 and 43 on therverticalside I6 and a second jumper 50 interconnects the terminals 44, 45, and46 and the terminals 2|, 22, and 23 on the vertical side I6. The fourthterminal I5 is wired by means of another jumper directly to the fourthterminal 24 the same as though the auxiliary line circuit were notincluded. Should it become 4desirable to equip the line A with anauxiliary circuit, this could be done by the simple actof disconnectingthe jumper 48 and connecting terminals 8, 9, and I0 to terminals 33, 34,and 35 by one jumper and connecting terminals 36, 31 and 38 to terminalsI1, I8 and I9 by a second jumper the same as shown' in connection withline B. Likewise any other subscribers line in the exchange may bechanged at any time to include an auxiliary line circuit.

The subscribers-lines are connected to the connector banks at thehorizontal side 5 of the intermediate distributing frame. The line B,for example, is shown connected to terminals of connector C-2 by thewiresV extending tothe terminals I2, I37 and I4. Likewise connections orterminals 8, 9, and I8 join the subscribers line A to the terminals ofthe connector switches.

The operation of the system shown in Fig. 1 will now be described. Whilethe individual line circuit is already well known in the art, it may behelpful rst to describe briefly the operation of the system when sowired'as not to include the auxiliary line circuit. Assume, therefore,that the subscriber of line A wishes to converse with the subscriber ofline E. When the calling subscriber removes his receiver, the line relay25 operates over an obvious circuit and energizes the nder start relay5|. The finder switch F starts and searches for the terminals of thecalling line, and, upon finding the same, it applies ground potentialAover conductor 52 through the right contact of the line relay 25 to thesleeve conductor 53. This operates the cut-off relay 26, which locks tothe grounded conductor 52 and disconnects the line relay from the tipand ring conductors of the line. The ground potential on conductor 53 isalso applied by way of conductor 54 to the test terminals in theconnector switches. From this point on the calling subscriber operateshis dial 55 in the well known manner to set selector switch S andconnector switch C to establish connection with the called subscribersline E. In case it is necesary to operate the calling subscribersregister 21, registering operating current is applied to the sleeveconductor 53 and iiows to register 21 over circuit extending by way ofterminals I9, I8, II and 28. After conversation the connection isreleased in the usual manner, the cut-01T relay 26 releases, and theequipment is thus restored to its normal condition.

Assume next that the subscriber of line B wishes to communicate with thesubscriber of line G. In this case the auxiliary line circuit AL-I isassociated with the calling; line B.

When ,the calling subscriber removes his receiver to initiate the call,a circuitis closed from battery .through the right winding of Vlinerelay'28, contact of cut-oli` relay 29, thence Yover middle jumper wire59, winding of controlrrelay 39, middle jumper wire 49, thence over the'loop' of subscribers line B and returning over the upper jumper wire 49to terminal 4|, thenceto terminal 44, right-hand jumper wire 50,terminal 2|, contact of cut-o relay 29, left winding of line relay 2B toground. Relays 28 and 39 operate in this circuit. Relay 39 immediatelyapplies ground potential over the lower jumper wire 49 by way ofterminal |4 to the test terminals of the connector switches, such asswitch C-2, having access to the calling line B. Thus the callingline isguarded against seizure by a connector switch as soon as the receiver isremoved from the switch-hook. Relay 28 operates the start relay 5B, andthe line nder F--I searches for and seizes the terminals of the callingline B. As soon as the terminals are seized,V ground potential isapplied to the sleeve conductor 51 by way of the right-hand contact ofrelay 28, operating relay 29. This ground potential also results inoperation of auxiliary relay 40, the circuit extending from batterythrough the winding of relay 4|), thence over the left-hand jumperwireV5|! to the grounded sleeve conductor 51. Relay 4|! closes a shuntaround the winding of relay 39. The cut-on? relay 29 in operatingreleases the line relay 28, and the tip and ring conductors of thesubscribers line B are now-extended through the terminals of the lineiinder F-l to battery and ground in the well known manner. The cutoffrelay 29 locks through its right front contact and maintains groundpotential on the conductor 51 to hold the relay 4|) operated. Relay 40thereby maintains a shunt around thewinding of relay 39 to prevent itfrom operating andvto exclude its winding from the circuit including thesubscribers loop. The subscribers line B is now maintained busy at theterminals of the connector switches by means of a circuit to ground overthe sleeve conductor 51 through thelefthand jumper Wire 50, back contactofrrelayf`39, thence as above traced to the test rterminals of theconnector switches. Following this the 'se-1 lector S-I and connectorC--I are operated in response to the subscribers dial to complete aconnection to the called line G. At the end of conversation theconnection is released, and ground `potential is removed from the sleeve:conductor 51. This restores the cut-off relay 29 and the auxiliaryrelay 40.

The next assumption to be made is that the subscribers line B has beenengaged in an established connection as a called line. It may beconsidered that 'the established connection involves a calling line D,line nder F-2, selector S--2, connector C--2 and the called line B. f Atthe time the connector C-Z set its brushes on the terminals of thesubscribers line B, cut-ofi relay 29 and auxiliary relay 40 wereoperated. The circuit for these relays are traced from battery to thewinding of relay 29 and from battery to the winding of relay 48, thencein parallel to the back contact of relay 39, lower conductor of jumper49, thence to ground over the sleeve terminals of the connector switchC-2. Relay 29 disconnects the line relay 28 from the tip and ringconductors and extends the grounded conductor 51 through its frontcontact to the terminals of the line lnderswitch 'F-L A furtherassumption to be made is that the release control of this connectionbetween lines D and B is `such v for accomplishing the same purpose.

thatwhen the calling 'subscriber Vhangs up his receiver the entireconnection, including connector C-2, is released. If, therefore,following the conversation, the calling` subscriber D is the rst toreplace his receiver, all switches, including the connector switch 0 2,release, leaving the called line B in the condition of a calling line.The release of the connector switch C-.2 removes the ground potentialfrom the test terminal, causing relays 29 and 49 to restore. The instantrelay 29`releases, itY connects the line relay 28 across the closed'loop of the subscribers line B. Relay 28 thereupon operates and startsthe line finder F-I to search for the terminals of the line B. As aboveexplained, the relay 39 also Operates in circuit with the relay 28, andrin so doing it applies ground potential to the test terminals in theconnector switches.

Thus a subscribers line is guarded by the relay 39in the connectorswitch bank during the time that his receiver is oif the switch-hook andbefore a line nder has seized his line. Should a connector switch 'bestepped to the terminals of his line during this interval, it would finda busy potential the Vsarne as though the suhscribers line were actuallyengaged in conversation. Either the busy signal can be returned to thecalling subscriber or, in the case of a private branch exchange group,the connector switch may step to a succeeding trunk.

Fig. 2 shows a somewhat different arrangement In this ligure thesubscribers line H appears in terminals |2| and |22 on the vertical side59 of the member 5|y of the main frame and in terminals 12 and 13 on thevertical member G3 of the intermediate frame'. 'IfoV wire thesubscribers line H in such a way as to include the auxiliary linecircuit AL-2 in circuit with the individual equipment L--2, theconnections are made as shown in the drawings. In this case theterminals |2| vand |22 are connected by means of a jumper |20 to theterminals 64 and 65, respectively. Also the terminals 1D and 1| areconnected by a second jumper 82 to the terminals 88 and 3|. Theterminals Scand 8i on the horizontal side of the mainframe areconnectedby a cable pair 19 to the terminals AS6 and B1, respectively,on the vertical side of the intermediate frame. If, on the other hand,it 'is desired to connect the subscribers line H directly to the linecircuit L-2, excluding the auxiliary circuit AT FZ, the jumper 82 isdisconnected from terminals 8l) and 8|, and the jumper |29 is nowconnected between terminals |2| and V|22 and terminals 89 and 3| Theoperation of the circuit shown in Fig. 2

will now be described. Assuming the subscribers line H initiates a callfor the purpose of obtaining connection with the subscriber of line J,theremoval of the calling partys receiver from the vswitch-hook operatesthe line relay 11. The circuit ior this. relay may be traced frombattery to the right winding thereof, contact of cut-off'relay 18,terminal 61, lower conductor of cable pair 19, terminal 8|, right-handconductor of jumper B2, terminal 1| to the winding of auxiliary relay83, terminal 65, thence over the loop of calling line H and returning toterminal B4, conductor 89, terminal 18, left-hand conductor of jumper82, terminal .88, upper conductor of cable pair .1.9,

terminal 66, throughk the contact of relay 18 and the left-hand windingof relay 11. to ground. The line relay 11 operates the start relay 85 tostart the line iinder F-3 to search for the terminals of the callingline. Relay 83 operates and applies ground potential over terminal 12,conductor 80, terminal 16, thence over the horizontal side 02 to thetest terminals of the connector switches, including connector C-4. Thisrenders the line busy to the connectors. The subscribers line V1s nowextended through the terminals of the line nder F-3 to battery andground in the well known manner. Relay 81,` in operating shunts therelay 83 and this latter relay releases. The line H is maintained busyat the connector switches by means of a circuit from ground over thesleeve conductor 86, thence over terminal 68, terminal 13, back contactof relay 83, terminal 12 and by way of conductor 88 as above traced tothe test terminals of the connector switches. The release of theconnection takes place in the usual manner.

When the subscribers line H is called by the subscriber of another line,such as line K, the connection is established by way of line iinderF--4, selector S-4 and connector C--4. As soon as the connector C-4engages the terminals of thecalled line H, ground potential is extendedfrom the connector over the conductor 88 through thev back contact ofrelay 83 and thence in parallel through the windings of relay 01 andcut-oli relay 10. Relay 81 operates and shunts the relay 83,7and relay18 operates and disconnects the line relay 11. The relay 83, beingvshunted by relay 81, is eiiectively excluded from the talkingconnection between the calling and called lines. The grounded sleeveconductor is also extended by way of the contact of relay 18 to the testterminals of the line nder switches.

Fig. 3 shows a still further modification for attaining somewhat thesame results as in Figs. l and 2. In this gure a subscribers line M isconnected from the main distributing frame to the horizontal side 90V ofthe intermediate frame and there appears in terminals 9|, 92 and 93.From these terminals the line is connected to the contactl banks of theconnector switches, such as connector C-5. The individual line circuitL-3 is connected to terminals 94, 95, and 96 on the vertical side 01 ofthe intermediate frame.- The auxiliary line circuit AL-3 is connected toterminals 08, 99 and |00 on frame member 00 and to terminals |0|, |02,and |03 on frame member 91. If it is desired to wire the subscribersline M directly rto its individual linecircuit L-3, this is accomplishedby disconnecting the jumper |04 from terminals 9|, S2 and 93 and bydisconnecting the jumper |05 from terminals 94, 95 and 96, and furtherby connecting the terminals 9|, 92 and 93 directly to terminals 94, 95and 96, respectively. If it is desired to include the auxiliary linecircuit AL3, the wiring shown in the drawings is used.

The operation of the circuit shown in Fig. 3 when wired to include theauxiliary line circuit will now be described. Assume that the subscriberof line M wishes to call the subscriber of line N. When the callingsubscriber initiates the call, a circuit is closed from battery throughthe right winding of the line relay |06, contact of 'cut-off relay |01,terminal 95, middle conductor of' jumper |05, terminal |02, lowerwinding of auxiliary relay |08, terminal 99, the middle conductor ofjumper |04, terminal 92, thence over the loop of the calling line andreturning to terminal 9|, leftl-hand conductor of jumper |04, terminal98, upper winding ofA relay |03,' terminal |0I, left-hand conductor ofjumper |05, terminal 94, thence through the contact of cut-off relay |01and the left winding of relay |06 to ground. yRelay Y|08 operates inthis circuit and in so doing disconnects the cut-Off relay |01 from thetest terminal'of the connector switches, including the connector switchC-5. Thus battery Vpotential is removed from the test terminals of theconnectors, and a connector arriving on the terminals of the line M atthis time does not nd the line` in condition for the application ofringing current thereto. The line relay |06 in operating operates thestart relay l0 to start the line finder F-5 in operation to seize theterminals of rthe calling line M. When the finder finds the line, groundpotential is applied over the sleeve conductor through the contact ofrelay |06 to conductor causing the operation of the cutoff relay |01.Ground on this conductor also results in the operation of relay |00. Theoperating circuit for the latter relay may be traced from batterythrough its winding, front contact of relay |08,- terminal |03,right-hand conductor of jumper |05 to the grounded conductor The relay|01 disconnects the line relay |06 and locks through its contact to thegrounded sleeve tor inthe line fin-der F-5, thence over conductorterminal 96, thence to terminal |03 through the back contact of'relay|08, terminal |00, righthand conductor of jumper |04, terminal 93 andthence to the multiple test terminals of the connector switches. Thesubscriber of line M may now operate his dial to set the selector switchS-5 and the connector switchY C-S to the terminals of the calledsubscribers line N. At the end of conversation the connection isreleased in the well known way.

Assume now that the subscriber of line P calls l 'the subscriber of lineM. In this event the connection is established by way of line iinderF-B, selector S-6 and connector C--5 to the terminals of the called lineM. When the connector 0 5 i.; reaches the terminals of the called lineM, a circuit is closed from ground in the connector switch over the testterminal thereof, thence to terminal 93, terminal |00, back contactfofrelay |08, terminal |03, terminal 06, to the winding of cut- 01T relay|01. Relay |01- operates, disconnects the line relay |06, and extendsthe grounded conductor through to the terminals of the line nderswitches, including inder F-5. Ifat the end of conversation the calledparty P is the rst to hang up his receiver, the entire connection may bereleased, including the connector switch C-5.l When ground potential isremoved from the sleeve conductor as the result of the release orconnector C-5, cut-off relay |01 releases and reconnects the line relay06 to the conductors of the subscribers line M, the receiver of which isstill oli the hook. Relay |00 operates in series with the closed loop ofthe line and starts the line nder F.5. Also relay |08 operates and asabove described disconnects battery potential from the test terminals ofthe connector switches. Should a connector arrive on lthe terminals ofthe line M while the line finder F-- is hunting for the line M, it wouldnd the line neither in a busy nor in an idle condition. Therefore, theconnector would wait until the line finder F-5 iinds the line M. At thistime the cut-o relay |01 operates and disconnects the line relay |06.Also relay |09 operates and shunts the relay |08 allowing it to release.Ground potential from the line nder is now extended over the sleevecircuit through the back contact of relay |08, thence to the testterminal of the connector switch C-5. However, if the waiting connectorhas already passed its busy test stage, it will not recognize thisground potential as a busy condition and will continue to wait on theterminals of the line M. As soon as the subscriber M replaces hisreceiver, the line finder F-5 is released, the grounded connection isremoved from the sleeve conductor, and relays |01 and |09 are released.Battery potential is now applied through the winding of cut-oli relay|01 to the testterminal of the waiting connector switch. This causes theconnector switch to function to apply ringing current to the subscribersline M, thus calling the subscriber back to his telephone.

The iinder switches, selector switches, and connector switches discloseddiagrammatically herein may be of any well-known type, such as theStrowger step-by-step switch. The speciiic circuits of the connectorswitches which have been referred to in some detail herein are disclosedand described in the patent to Newforth 2,005,844, granted June 25,1935.

What is claimed is:

l. In a telephone system, a distributing frame having a horizontalterminal member and a vertical terminal member, a plurality of linesconnected to said horizontal member, a plurality of line circuitsconnected to said vertical member, said line circuits being individualrespectively to said lines, a plurality of control circuits connectedonly to said vertical member, and cross-connecting conductors for saidhorizontal and vertical members for connecting any one of said lines toits individual line circuit either directly or through any one of saidcontrol circuits.

2. In a telephone system, a line finder switch, a connector switch, asubscribers line appearing in terminals of said nder and also interminals of said connector, a line relay connected to the conductors ofsaid line, a cut-off relay for disconnecting said line relay from saidline, means responsive to the closure of the subscribers line to setsaid finder in operation to iind the line, an auxiliary relay includedin the circuit of said line at a point between the substation and saidline relay,` said auxiliary relay serving to render the lineunselectable to said connector switch while said finder is in operation,and means for disabling said auxiliary relay.

3. In a telephone system, a line nder switch, a connector switch, asubscribers line appearing in terminals in said line iinder switch andalso in terminals in said connector switch, a line relay connected tothe talking conductors of said line,v

means controlled by said line relay for setting said finder switch inoperation to seize said line,

4a control relay connected in circuit with said line at a point betweenthe substation of the line and said line relay, said control relayserving to render the line unselectable to said connector switch, acut-off relay operable when the line finder finds the line to disconnectsaid line relay from said line, and circuit means controlled by saidcut-oil relay for shunting said control relay.

4. In a telephone system, a line finder switch, a connector switch, adistributing frame having horizontal and vertical members, a subscribersline connected to said horizontal member, a line circuit individual tosaid line including a line relay and a cut-ofi relay, said line circuitbeing connected to said Vertical member and also appearing in terminalsin said nder switch, an auxiliary circuit including a control relayconnected to said Vertical member, a set of conductors interconnectingsaid horizontal member and the terminals of said connector switchindividual to said line, cross-connecting conductors for conl nectingsaid line to said auxiliary circuit and to said line circuit, meanseiiective when said line is in a calling condition for operating saidline relay and said control relay, said line relay serving to start saidline iinder in operation to seize said line, said control relay servingto render the line non-selectable to said connector switch, and meanseiective when the line inder finds the line for operating said cut-offrelay to disable the line relay and for shunting said control relay tocause its release.

5. In a telephone'system, a plurality of lines, a switch for seizingsaid lines, line circuits individual respectively to said lines, eachline circuit having a line relay, an auxiliary circuit including acontrol relay arranged to cooperate with any one of said line circuits,cross-connecting means for connecting said auxiliary circuitindividually to any particular one of said lilies` and to the linecircuit of such line, a circuit for energizing simultaneously the linerelay of said particular line and the control relay of said auxiliarycircuit to cause said switch to seize said particular line and to guardsaid line until it is seized, and circuit means rendered effective bytheline circuit of the seized line to cause the release of said auxiliarycircuit relay.

6. In a telephone system, a plurality of lines, trunk circuits,non-numerical switches for interconnecting saidV lines and trunkcircuits, line circuits individual respectively to said lines, each linecircuit having a line relay, terminals for said lines and a selectorswitch for seizing said terminals, an auxiliary circuit including acontrol relay arranged to cooperate with any one of said line circuits,cross-connecting means for connecting said auxiliary circuitindividually to any particular one of said lines and to the line circuitof such line, a circuit for energizing the line relay of said particularline and the control relay of said auxiliary circuit to cause anon-numerical switch to interconnect said line and one of said trunkcircuits, circuit means closed by said control relay for placing a busycondition on the terminals of said particular line to guard it until thenon-numerical switch has completed its function, and circuit meansrendered eiective by the line circuit to cause the release of saidcontrol relay.

MARCELLUS BALLI MCDAVITI.

